The aqueous microemulsions according to the invention can be transformed to other compositions such as aerosols by using suitable auxiliary materials.
It is known that synthetic pyrethroids are used to a continuously increasing extent in the state of the art plant protection since a satisfactory protection can be achieved by applying the active ingredient in amounts as low as 10 to 100 g/ha and on the other hand, the residue of the active ingredient becomes negligible within a relatively short time of decomposition. The pyrethroid-type active ingredients are used in the form of wettable powders (WP), suspension concentrates (FW) and most frequently as microemulsion compositions (EC). General demands made on the state of the art emulsion concentrates comprise
a) ensuring the very dilute emulsion phase state in the concentration for application by an economical amount [75 to 150 g/liter (abbreviated: g/l] of a surface active agent; and PA1 b) avoiding the use of xylene as solvent because of problems connected with safety, environmental protection and phytotoxicity. PA1 above 95% in 0.01% concentration, PA1 above 90% in 0.1% concentration and PA1 above 85% in 1% concentration
The low amount of the surface active agent can be ensured by a suitable selection of state of the art surface active substances. For replacing xylene, the solvent manufacturers developed specific but expensive novel types of solvents whereas the formulating manufacturers made efforts to replace the solvents by aqueous systems. Thus, in the German patent specification NO. 3,235,612, aqueous microemulsions are described which contain: 0.1 to 80% by weight of active ingredient together with 1 to 20% by weight of a particular emulsifier mixture and optionally 1 to 30% by weight of organic solvent, being partly miscible with water; as well as water. The particular emulsifier is a mixture of an alkylaryl polyglycol ether with an alkylarylsulfonate salt. The emulsion stability of the emulsion concentrates reported in the German patent specification No. 3,508,643 is ensured by polyvinyl alcohol and an organic acid. The aqueous microemulsions described in the German patent specification No. 3,624,910 contain as emulsifiers a phenol or a phenolate salt substituted by ethoxylated and phosphorylated styryl group in combination with one or more non-phosphorylated emulsifying agent(s) together with 5 to 30% by weight of an usual solvent.
The aqueous microemulsions set forth in the published European patent application No. 0,160,182 contain pyrethroids and phosphoric acid esters as active ingredients and ethoxylated tristyrylphenol, ethoxylated distyrylphenol-ammonium sulfate and an alkylarylsulfonate as emulsifying agents. Emulsion concentrates containing low molecular aliphatic alcohols and ketones as stabilizing agents are described in the published Japanese patent application No. 51-59778.
Another problem of the EC-type compositions arises in that a stable spray liquid, required to remain stable in most cases for at least 24 hours, has to be prepared from the given emulsion concentrates by using waters with various hardnesses. In addition, synthetic pyrethroids are weakly soluble in aliphatic hydrocarbons and apolar solvents which in turn are preferred from the viewpoint of phytotoxicity, environmental protection and safety; thus, they can meet the criterion of the cold-resistance only with difficulties.